In current advanced technology nodes, where the critical dimensions of devices scale down to sub 10 nm, their structural integrity can be greatly affected by the presence of defects, surface and interface stresses due to their large surface to volume ratio. This is especially the case for high aspect ratio FinFET or memory structures subjected to a wet processing step, where their stability is determined by the competition between the capillary interactions/surface adhesion of the solvent and the mechanical rigidity of the structures. In cases where the interaction with the solvent dominates the mechanical integrity of the device, the structure undergoes a pattern collapse process, which can hardly be recovered. Therefore, to find the ultimate limit of scaling for damage-free wet processing, it is important to understand the mechanical properties and the nature of the physicochemical interactions that occur at the nanoscale. This Ph.D. topic aims providing this understanding by combining different modeling approaches that will provide insights into the mechanisms that drive the process at both the macroscopic and at the atomistic scales.
With that respect, atomistic simulations are powerful tools to model and quantify the impact of surface functionalization, the stress/strain distribution in nanostructures and help studying their deformation and fracture mechanisms. In this Ph.D. project, the mechanical property of nanostructures will be studied by molecular dynamics simulations and the impact of reduced dimensions, material stacks, structural profiles and surface functionalization on the mechanical rigidity will be systematically investigated.
Capillary interactions around densely packed nanostructures are another important aspect in the process of a pattern collapse. In a second phase, this work will also focus on the modeling of the 3D capillary surfaces around various structures with different geometries and surface materials. As a liquid surface always evolves to minimize its surface area, the equilibrium shape of liquid meniscus will be calculated based on total energy minimization. Capillary interactions will then be studied for different structure profiles, dimensions and wetting properties. The obtained simulation results will then be compared with the mechanical rigidity of nanostructures established previously to get the stability limit.
Finally, roads to minimize the pattern collapse process will be investigated. Surface functionalization of high aspect ratio structures by organic monolayers is a popular approach used to reduce the surface adhesion and the pattern collapse. It is however very challenging to design an effective surface chemistry that prevents completely the collapsing process due to the complex physiochemical interactions that occur in solutions. Here too, molecular dynamics simulations will be used to investigate the nature of the intermolecular interactions of surfaces functionalized by organic molecules in presence different solvents. The obtained results will be used to tailor their chain length and end groups to help designing strategies to reduce the collapsing process.
Required background: Imec will provide training to both UNIX/Linux and to the material modeling techniques. A strong motivation and background in mathematics and physics are required. Excellent writing and oral communication skills are desired. Some basic programming skills are a plus.
Type of work: 10% literature, 90% modeling
Supervisor: Stefan De Gendt
Daily advisors: Xiumei Xu, Geoffrey Pourtois
The reference code for this PhD position is STS1712-42. Mention this reference code on your application form.